1. Field of the Invention
The present invention relates to a hydraulic arrangement by which a plurality of so shift rails of a transmission, in particular a double clutch transmission, can be actuated, the arrangement including one double acting cylinder per shift rail by which the respective shift rail can be actuated to move back and forth.
2. Description of the Related Art
Hydraulic arrangements for hydraulically controlling and supplying a is transmission are known. In automatic transmissions like, e.g., shift transmissions, CVT transmissions, or dual clutch transmissions with hydraulic control, this means that for actuator control, like clutch actuator- or shift actuator control and cooling-/lubrication an oil supply (typically a pump with a pump drive) is required.
Typically, the pump drive is a mechanical pump drive that is coupled to the internal combustion engine. In modern transmissions, this mechanical pump drive can be supplemented with an E-pump arrangement (this means an electric motor with a pump).
Furthermore, oil supplies are known in which the transmission and clutch actuators operate without a mechanically driven pump. Herein, however, due to the configuration of the clutch (this is a dry clutch), no cooling oil is required.
In dual clutch transmissions, so-called shift rails are used for shifting the gears. The shift rails in order to perform their functions, namely shifting a gear, have to be moveable in both directions along an axis. This movement can be provided, e.g., with hydraulic actuators which have to be hydraulically controlled accordingly. The shift rail can thus have a neutral position in the center of its travel, and can have a shifting position for a gear proximal to the respective ends of the travel.
The hydraulic actuators for moving the shift rails recited above can be configured as single acting cylinders or as double acting cylinders. Two hydraulic operating surfaces are required per shift rail, wherein the operating surfaces are implemented in the cylinders. The hydraulic operating surfaces per shift rail can have either identical sizes or different sizes. Depending on the surface concept, different hydraulic controls are required. Thus, the hydraulic operating surfaces can be arranged in two independent cylinders or in a double acting cylinder.
The operating conditions occurring when controlling the partial transmissions by transmission actuators or shift rails are quite different. Thus, situations with high volume flow and low pressure requirement, as well as situations with high pressure and low volume flow requirement, are provided. During a shifting process, initially a large travel has to be covered at low pressure (this means high volume flow with low pressure), and from the beginning of the synchronization shortly before shifting a gear a small travel with higher resistance has to be covered, which means low volume flow with high pressure has to be covered.
In known arrangements of hydraulic systems for hydraulically controlling a dual clutch transmission with a first partial transmission and a second partial transmission, the operating surfaces of such arrangement are respectively controlled with a valve function group. When a pressure control and a volume control is provided per operating surface, then conventionally eight valves are required for four shift rails, e.g., for eight gears (seven forward gears and one reverse gear). Assemblies are also known which implement this function with five valves or with one valve in the form of a multiplexer (e.g., configured as a rotating valve). These approaches have cost and/or functional disadvantages.
Thus, it is an object of the present invention to provide an improved hydraulic system by which a control of a transmission is provided with as few hydraulic components as possible, in particular a dual clutch transmission.